Cyclotron and Synchrotron Radiation
Radiation emitted by electrons gyrating in the magnetic field, a loss that grows with field and temperature.
Radiation from gyration
Electrons spiraling around magnetic field lines are constantly accelerating (their direction changes), so they radiate at the cyclotron frequency and its harmonics. At the mildly relativistic temperatures of fusion plasmas this becomes synchrotron radiation, spread over many harmonics. The emitted power per electron scales as:
P_cyc ~ B^2 T_e (relativistic corrections grow with T_e)The strong dependence on B^2 means cyclotron losses matter most in high-field devices and at high electron temperature.
Reabsorption and reflection
Unlike bremsstrahlung, much cyclotron radiation is reabsorbed by the plasma itself (the plasma is optically thick at low harmonics) and reflected back by the metallic walls. The net loss is therefore far smaller than the raw emission and depends on wall reflectivity and plasma opacity, making it harder to estimate.
Why it matters at high field
- High-field, high-temperature designs must account for net cyclotron losses
- Wall reflectivity is a real engineering parameter in the loss estimate
- At very high T_e, cyclotron losses can rival bremsstrahlung
How it is computed
Because of reabsorption, cyclotron loss is computed with radiation-transport models (for example the Trubnikov formula or full transport solvers) that account for the harmonic structure, plasma opacity, and wall reflection coefficient, rather than a simple emission integral.
Design relevance
In strong-field devices the net cyclotron loss enters the power balance alongside bremsstrahlung. For the high-field Hyperion breeder (16.84 T peak, 8 T on-axis) and especially for high-field, high-temperature concepts, net cyclotron radiation is one of the loss channels evaluated with reflection assumptions in the design-point power balance.